Abstract

This paper presents an x-ray study of GaN, which is grown on nominally undoped and oxygen-doped AlNnucleation layers on sapphire substrates by metal organic vapor phase epitaxy. Without additional oxygen doping a trimodal nucleation distribution of AlN is observed leading to inhomogeneous in-plane strain fields, whereas in oxygen-doped layers a homogeneous distribution of nucleation centers is observed. In both types of nucleation layers extremely sharp correlation peaks occur in transverse -scans which are attributed to a high density of edge-type dislocations having an in-plane Burgers vector. The correlation peaks are still visible in the (0002) -scans of 500 nm GaN which might mislead an observer to conclude incorrectly that there exists an extremely high structural quality. For the undoped nucleation layers depth-sensitive measurements in grazing incidence geometry reveal a strong thickness dependence of the lattice parameter , whereas no such dependence is observed for doped samples. For oxygen-doped nucleation layers, in cross-sectional transmission electron microscopy images a high density of stacking faults parallel to the substrate surface is found in contrast to undoped nucleation layers where a high density of threading dislocations is visible. GaN of grown on top of 25 nm AlNnucleation layers with an additional in situ SiN mask show full widths at half maximum of and in (0002) and (10–10) high-resolution x-ray diffraction-scans, respectively.

This research was partly funded by Osram Opto Semiconductors and the Bundesministerium für Bildung und Forschung (BMBF). The authors would like to thank T. Fuchs and M. Grimm for expert assistance in the SIMS analysis and Quincy Liu for critical reading of the manuscript.